import datetime

from django.db import connection
from django.db.models.query import QuerySet, Q
from django.utils.timezone import now as timezone_now

from sqlalchemy.sql import (
    column,
    literal,
    func,
)

from zerver.models import (
    Message,
    Recipient,
    UserProfile,
)

from typing import Any, Dict, List, Tuple

# Only use these constants for events.
ORIG_TOPIC = "orig_subject"
TOPIC_NAME = "subject"
TOPIC_LINKS = "subject_links"
PREV_TOPIC = "prev_subject"

# This is used in low-level message functions in
# zerver/lib/message.py, and it's not user facing.
DB_TOPIC_NAME = "subject"
MESSAGE__TOPIC = 'message__subject'

def topic_match_sa(topic_name: str) -> Any:
    # _sa is short for Sql Alchemy, which we use mostly for
    # queries that search messages
    topic_cond = func.upper(column("subject")) == func.upper(literal(topic_name))
    return topic_cond

def filter_by_exact_message_topic(query: QuerySet, message: Message) -> QuerySet:
    topic_name = message.topic_name()
    return query.filter(subject=topic_name)

def filter_by_topic_name_via_message(query: QuerySet, topic_name: str) -> QuerySet:
    return query.filter(message__subject__iexact=topic_name)

def save_message_for_edit_use_case(message: Message) -> None:
    message.save(update_fields=["subject", "content", "rendered_content",
                                "rendered_content_version", "last_edit_time",
                                "edit_history"])

def update_messages_for_topic_edit(message: Message,
                                   propagate_mode: str,
                                   orig_topic_name: str,
                                   topic_name: str) -> List[Message]:
    propagate_query = Q(recipient = message.recipient, subject = orig_topic_name)
    # We only change messages up to 2 days in the past, to avoid hammering our
    # DB by changing an unbounded amount of messages
    if propagate_mode == 'change_all':
        before_bound = timezone_now() - datetime.timedelta(days=2)

        propagate_query = (propagate_query & ~Q(id = message.id) &
                           Q(pub_date__range=(before_bound, timezone_now())))
    if propagate_mode == 'change_later':
        propagate_query = propagate_query & Q(id__gt = message.id)

    messages = Message.objects.filter(propagate_query).select_related()

    # Evaluate the query before running the update
    messages_list = list(messages)
    messages.update(subject=topic_name)

    for m in messages_list:
        # The cached ORM object is not changed by messages.update()
        # and the remote cache update requires the new value
        m.set_topic_name(topic_name)

    return messages_list

def generate_topic_history_from_db_rows(rows: List[Tuple[str, int]]) -> List[Dict[str, Any]]:
    canonical_topic_names = {}  # type: Dict[str, Tuple[int, str]]

    # Sort rows by max_message_id so that if a topic
    # has many different casings, we use the most
    # recent row.
    rows = sorted(rows, key=lambda tup: tup[1])

    for (topic_name, max_message_id) in rows:
        canonical_name = topic_name.lower()
        canonical_topic_names[canonical_name] = (max_message_id, topic_name)

    history = []
    for canonical_topic, (max_message_id, topic_name) in canonical_topic_names.items():
        history.append(dict(
            name=topic_name,
            max_id=max_message_id)
        )
    return sorted(history, key=lambda x: -x['max_id'])

def get_topic_history_for_stream(user_profile: UserProfile,
                                 recipient: Recipient,
                                 public_history: bool) -> List[Dict[str, Any]]:
    cursor = connection.cursor()
    if public_history:
        query = '''
        SELECT
            "zerver_message"."subject" as topic,
            max("zerver_message".id) as max_message_id
        FROM "zerver_message"
        WHERE (
            "zerver_message"."recipient_id" = %s
        )
        GROUP BY (
            "zerver_message"."subject"
        )
        ORDER BY max("zerver_message".id) DESC
        '''
        cursor.execute(query, [recipient.id])
    else:
        query = '''
        SELECT
            "zerver_message"."subject" as topic,
            max("zerver_message".id) as max_message_id
        FROM "zerver_message"
        INNER JOIN "zerver_usermessage" ON (
            "zerver_usermessage"."message_id" = "zerver_message"."id"
        )
        WHERE (
            "zerver_usermessage"."user_profile_id" = %s AND
            "zerver_message"."recipient_id" = %s
        )
        GROUP BY (
            "zerver_message"."subject"
        )
        ORDER BY max("zerver_message".id) DESC
        '''
        cursor.execute(query, [user_profile.id, recipient.id])
    rows = cursor.fetchall()
    cursor.close()

    return generate_topic_history_from_db_rows(rows)

def get_topic_history_for_web_public_stream(recipient: Recipient) -> List[Dict[str, Any]]:
    cursor = connection.cursor()
    query = '''
    SELECT
        "zerver_message"."subject" as topic,
        max("zerver_message".id) as max_message_id
    FROM "zerver_message"
    WHERE (
        "zerver_message"."recipient_id" = %s
    )
    GROUP BY (
        "zerver_message"."subject"
    )
    ORDER BY max("zerver_message".id) DESC
    '''
    cursor.execute(query, [recipient.id])
    rows = cursor.fetchall()
    cursor.close()

    return generate_topic_history_from_db_rows(rows)